MOVIE REVIEWS : Arnold’s Mommy Syndrome : ‘Junior’ stars Schwarzenegger, Danny DeVito and Emma Thompson in a farce that opts for a traditional take.

Accomplished farceurs specialize in making the ridiculous plausible, and certainly few films can claim to be as unlikely as “Junior.” In cheeky defiance of the laws of nature, it presents us with the spectacle of ultimate male Arnold Schwarzenegger heavy with child. If the French had thought of it first, it might’ve been called “One Man and a Baby.”

“Junior,” however, is quintessentially studio American, which means it is as slickly commercial as the audience-pleasing proclivities of director Ivan Reitman (“Ghostbusters,” “Dave”) can make it. The jokes in the Kevin Wade and Chris Conrad script flow smoothly, and everything is as polished and smooth as a ballroom dance floor.

And in Schwarzenegger, Danny DeVito and Emma Thompson, the film has an expert cast whose comic gifts are always complementary. Schwarzenegger’s deadpan delivery, DeVito’s insistent miniature swagger and Thompson’s practiced slapstick clumsiness play off each other in satisfying three-part harmony.

The result is, of course, effective, but despite the trio’s fine efforts “Junior” can’t get past lightly amusing, never manages to work up a sustained comic head of steam. It is a farce without staying power, partly because of the traditional way it deals with its central theme.

Initially, however, it is fun to watch these three develop their characters. Schwarzenegger plays the bookish, barely human Dr. Alexander Hesse, a research scientist at San Francisco’s Lufkin Biotec Research Center whose motto is “Luck is for the ill-prepared.” His partner, gynecologist Dr. Larry Arbogast (DeVito), is frantic, effusive and perpetually exasperated with Hesse, who he sees as having “all the warmth and charm of a wall-eyed pike.”

Together, however, these men have developed what they consider a break through drug that prevents miscarriages. But when the FDA refuses to sanction Expectane, Lufkin administrator Noah Banes (Frank Langella) cancels Hesse’s grant and gives his lab space to the daft, socially maladroit Dr. Diana Reddin (Thompson), who specializes in freezing eggs.

Hesse is ready to head back to the fatherland, but Arbogast is more stubborn. Why not, he asks his partner, test the drug on yourself, as did Jenner, the discoverer of vaccination, by having a fertilized embryo implanted in your abdomen? “Come claim your place in the pantheon,” he cries, and Hesse, unable to resist such eloquence, begins one of the most cockeyed experiments in medical history.

While Schwarzenegger and DeVito improve on the comic timing they began in Reitman’s “Twins,” Thompson, an Oscar winner for the very different “Howards End,” shows she hasn’t forgotten the antic comic roots she displayed in 1989’s underappreciated “The Tall Guy.” And it is always satisfying to see the underutilized Pamela Reed, here cast as Arbogast’s pregnant ex-wife.

Given how well these actresses do, it is surprising that one of the things “Junior” stumbles over is how it treats Alex Hesse’s character when he does become pregnant.

Simply put, the stiff doctor melts into a compilation of cliched female behavior, crying at sentimental TV commercials, complaining about having nothing to wear and whining, “Does my body disgust you?” to anyone who will listen.

On one level, helped by Schwarzenegger’s performance, this is certainly innocent fun. But if it’s no longer acceptable for white folks to don makeup and mimic black behavior, or for males to prance around being cliched, limp-wristed gays, it is an interesting question why this kind of comedy remains more than acceptable.

To put this in a different perspective, it is helpful to remember back to Dustin Hoffman’s deft role in “Tootsie.” He, too, wore a dress and came to understand things about the opposite sex he hadn’t before, but that film treated him as a most unusual woman, not as a nonstop cliche. “Junior” doesn’t have the wit or the vision to try for something like that, and the feeling is inescapable that it would be a stronger film if it had.

* MPAA rating: PG-13, for sex-related humor. Times guidelines: It includes mostly gleeful stereotyping.

‘Junior’

Arnold Schwarzenegger: Dr. Alexander Hesse Danny DeVito: Dr. Larry Arbogast Emma Thompson: Dr. Diana Reddin Frank Langella: Noah Banes Pamela Reed: Angela Judy Collins: Naomi A Northern Lights production, released by Universal Pictures. Director Ivan Reitman. Producer Ivan Reitman. Executive producers Joe Medjuck, Daniel Goldberg, Beverly J. Camhe. Screenplay Kevin Wade and Chris Conrad. Cinematographer Adam Greenberg. Editor Sheldon Kahn, Wendy Greene Bricmont. Costumes Albert Wolsky. Music James Newton Howard. Production design Stephen Lineweaver. Art director Gary Wissner. Set decorator Clay A. Griffith. Set designers Barry Chusid, Dawn Snyder. Running time: 1 hour, 50 minutes.

* In general release throughout Southern California.